Electronic device, semiconductor device comprising such a device and method of manufacturing such a device

ABSTRACT

The invention relates to an electronic device comprising an electronic component  2, 3,  such as a SAW (=Surface Acoustic Wave) filter  2, 3  having connection areas  4, 5.  The filter  2, 3  is sealed off from the environment by means of a cover  6  forming a cavity  7  above the filter  2, 3.    
     According to the invention, the cover  6  is formed by a lacquer layer  6 A which is provided, at the location of the filter  2, 3,  with an opening  7′  and which is covered with a photoresist layer  6 B closing the opening  7′  such that the cavity  7  thus formed has a thickness above zero everywhere above the filter  2, 3.  This enables an accurate and stable frequency selection by means of the filter  2, 3  and allows the device according to the invention to be very compact and easy to manufacture. Thus, the device according to the invention is very suitable for use in an application such as a mobile telephone, also after integration of the device with a semiconductor device. The photoresist layer  6 B and the lacquer layer  6 A preferably contain further openings  8,  at the location of the connection regions  4, 5,  which are provided with bumps  9,  preferably solder bumps  9.    
     Preferably, the photoresist layer  6 B comprises a solid foil  6 B, which is solder-repellent. The invention also comprises a method of manufacturing a device according to the invention as well as a semiconductor device wherein the device according to the invention is integrated.

[0001] The invention relates to an electronic device comprising a bodyincluding a substrate on which at least one electronic component issituated, which electronic component is connected to one or moreconnection areas and is sealed off from the environment by means of acover on the component, which cover is provided on the substrate andforms a cavity above said component, said cover comprising a first body,which is situated on the substrate and which is provided, at thelocation of the component, with an opening, and said cover comprising asecond body, which is situated on the first body and closes the opening.If the component comprises an acoustic wave filter, such a device isadvantageously used in, inter alia, mobile telephones. The inventionalso includes a semiconductor device provided with such a device and amethod of manufacturing such a device.

[0002] Such a device is disclosed in European patent 0.367.181,published on 20.04.1994. In said document, a description is given of anacoustic wave filter formed in and on a piezoelectric substrate ofLiTaO₃. Said filter is sealed off from the environment by a coverprovided on the substrate, which cover forms a cavity above the filter.As a result, the filter is protected against dust and other influencesfrom the environment, such as attenuation, so that an accurate andstable frequency selection is possible. Said cover comprises, forexample, a synthetic resin cap or a ring onto which a metal plate issecured.

[0003] A drawback of the known device resides in that it is not verycompact and cannot be readily integrated in a semiconductor device.

[0004] Therefore, it is an object of the invention to provide a devicethat is compact and that can be readily integrated in a semiconductordevice and that is also easy to manufacture.

[0005] To achieve this, a device as described in the opening paragraphis characterized in accordance with the invention in that the first bodycomprises a lacquer layer, and the second body comprises a photoresistlayer, and the lateral dimensions of the opening as well as thethickness and the material of the second photoresist layer are chosen tobe such that the thickness of the cavity is above zero throughout thesurface of the component.

[0006] The invention is first of all based on the recognition that theuse of (photo)resist layers enables the thickness of the cover to bevery small, so that the device in accordance with the invention can bevery compact as a result of, in particular, a small thickness and hencecan particularly suitably be integrated on a semiconductor device thatis used, for example, in a mobile telephone. In addition, the inventionis based on the surprising recognition that a suitable choice of thethickness and the material of a photoresist layer enables, atpredetermined lateral dimensions of the cavity to be formed, this cavityto be formed in a thickness above zero throughout the surface area ofthe component. This is very important, in particular, in connection withan accurate and stable frequency selection of an acoustic filter. Theuse of a photoresist for the uppermost layer of the cover additionallyhas the important advantage that this layer can be readily provided withfurther openings, by means of photolithography, at the location of theconnection areas of the component. For this purpose, also the lacquerlayer is provided, at the same locations, with a further opening.

[0007] Consequently, in an important embodiment, also the lacquer layercomprises a photoresist, and further openings are situated in thelacquer layer and in the photoresist layer at the location of theconnection areas of the electronic component, in which openings contactbumps are situated on the connection areas. As a result, the device canbe very readily integrated, namely by means of a surface mountingtechnique, with a semiconductor device which comprises, for example, ahigh-frequency circuit. Preferably, the contact bumps comprise a solderand, in connection therewith, the photoresist layer, and preferably alsothe lacquer layer, is a solder-repellent layer.

[0008] In a preferred embodiment, the lacquer layer and the photoresistlayer comprise a solid foil. It has been found that such a foil can mostsuitably be used to satisfy the necessary requirements of the invention.Besides, such a foil can readily satisfy the requirement that it shouldbe solder-repellent.

[0009] Preferably, the electronic component comprises a surface acousticwave filter. On the one hand, the invention enables an accurate, stablefrequency selection of such a filter, on the other hand, a compactintegration of such a filter is very important to many applications,such as mobile telephony.

[0010] Therefore, the invention also comprises a semiconductor devicewhich includes a semiconductor body with a substrate, and which isprovided with one or more semiconductor elements provided with anelectronic device in accordance with the invention.

[0011] The invention further comprises a method of manufacturing anelectronic device comprising a body including a substrate on which atleast one electronic component is formed, which electronic component isprovided with one or more connection areas and is sealed off from theenvironment by providing the component with a cover on the substrate, acavity being formed above the component, and said cover being formed byproviding a first body on the substrate and providing said body with anopening at the location of the component, and by providing a second bodyon the first body, resulting in the opening being closed, which methodis characterized in accordance with the invention in that the first bodyis formed by applying a lacquer layer on the substrate, and the secondbody is formed by applying a photoresist layer on top thereof, and thelateral dimensions of the opening, and the material and the thickness ofthe photoresist layer are chosen to be such that the thickness of thecavity is above zero throughout the surface area of the component.

[0012] Preferably, also for the lacquer layer use is made of aphotoresist, and further openings are formed in the lacquer layer and inthe photoresist layer at the location of the connection areas of theelectronic component, in which openings contact bumps, preferablycontaining a solder, are formed on the connection areas. For the lacquerlayer and for the photoresist layer use is preferably made of a solidfoil, which is preferably solder-repellent. If for the electroniccomponent use is made of a surface acoustic wave filter, a method inaccordance with the invention enables an attractive device in accordancewith the invention to be obtained in a very simple manner.

[0013] These and other aspects of the invention will be apparent fromand elucidated with reference to the embodiment(s) describedhereinafter.

[0014] In the drawings:

[0015]FIG. 1 is a diagrammatic, perspective view of an electronic devicein accordance with the invention,

[0016]FIG. 2 is a diagrammatic, cross-sectional view, at right angles tothe thickness direction, and taken on the line II-II, of the deviceshown in FIG. 1, and

[0017]FIGS. 3 through 7 are diagrammatic, perspective views of thedevice shown in FIG. 1 in successive stages of the manufacturing processusing a method in accordance with the invention.

[0018] The Figures are diagrammatic and not drawn to scale; particularlythe dimensions in the thickness direction being exaggerated for clarity.Like reference numerals refer to like areas whenever possible.

[0019]FIG. 1 is a diagrammatic, perspective view of an electronic devicein accordance with the invention, and FIG. 2 is a diagrammatic,cross-sectional view, at right angles to the thickness direction andtaken on the line II-II, of the device shown in FIG. 1. The devicecomprises a body 10 including a 0.5 mm thick substrate 1 which, in thiscase, is made of LiTaO₃. As shown in FIG. 2, a metal layer 2, 3, 4, 5 ofaluminum is provided thereon in a thickness of 0.3 μm, said metal layercomprising the following parts: a first electronic component 2 which, inthis case, includes two enmeshing comb-shaped conductor patterns, whichare not separately shown in the Figures, said first electronic componentand the substrate 1 jointly forming a first acoustic wave filter 2. Thelength and the width of the teeth of the filter are, respectively, 1 mmand ?μm, the spacing between the teeth is 2 μm, and the number of teethis of the order of several hundred. The filter 2, i.e. the twocomb-shaped portions thereof, is provided with two connection areas 4A,4B. The metal layer 2, 3, 4, 5 additionally comprises a second filter 3,which resembles the first filter 2, but the comb structures thereofcomprise a different, yet comparable, number of teeth, said secondfilter being provided with two further connection areas 5A, 5B. For moredetails regarding the structure and operation of these so-called SAW(=Surface Acoustic Wave) filters, reference is made to the magazine “OkiTechnical Review”, No. 158, vol. 63, April 1997. The filters 2, 3 aresealed off from the environment by means of a cover 6 which is providedon the substrate I so as to form a cavity 7 above the filters 2, 3, i.e.in this case two cavities 7. The cover 6 comprises a first body 6A,which is provided with an opening 7′ at the location of the filters 2,3, and a second body 6B, which closes the openings 7′, is provided onsaid first body.

[0020] In accordance with the invention, the first body 6A comprises alacquer layer 6A, and the second body 6B comprises a photoresist layer6B, and the lateral dimensions of the opening 7′ and the thickness andthe material of the photoresist layer 6B are chosen to be such that thethickness of the cavity 7 is above zero throughout the surface of thecomponent 2, 3. The use of a lacquer layer 6A and a photoresist layer 6Benables the thickness of the cover to be very small, so that the devicein accordance with the invention is very compact and hence particularlysuitable for integration on a semiconductor device for, for example, amobile telephone. The invention is also based on the recognition that asuitable choice of the thickness and the material of the photoresistlayer 6B in combination with a suitable choice of the lateral dimensionsof the openings 7′ in the lacquer layer 6A enables, at given dimensionsof the component 2, 3, this component to be situated, throughout thesurface, below a cavity 7 having a thickness which is larger than orequal to zero. By virtue thereof, an accurate and stable frequencyselection by means of the filters 2, 3 is possible, which is veryimportant for the intended applications. The use of a photoresist layer6B for the second body 6B has the additional important advantage thatthis layer 6B can be readily provided with further openings 8, forexample by means of photolithography, for example at the location of theconnection areas 4, 5 of the filters 2, 3. It has been found that asuitable lacquer layer 6A is a layer 6A of Conformal 2523 having athickness of approximately 58 μm. For the photoresist layer 6B use canadvantageously be made of an approximately 32 μm thick layer 6B ofLaminar 5032. By virtue thereof, deflection of the photoresist layer 6B,at the chosen dimensions of the filters 2, 3, i.e. a width of 1 mm and alength of several mm, is limited to less than 20% of the thickness ofthe lacquer layer 6A. It is to be noted that the most critical dimensionas regards deflection is the smallest dimension of the filter 2, 3, i.e.in this case the width. The overall surface area of the device rangesfrom approximately 2×3 to 3×4 mm².

[0021] For the lacquer layer 6A use can also advantageously be made,like in this example, of a photoresist layer 6A, which enables theopenings 7′ and any further openings 8 to be readily formed therein.Said further openings 8 and the openings in the photoresist layer 6B canthen be formed simultaneously. It is alternatively also possible to formthe desired openings 7′, 8 in the lacquer layer 6A when said lacquerlayer is applied, for example by applying the lacquer layer 6A by meansof a screen printing technique. In this example, the device alsocomprises ground connections 11A, 11B, which are provided at thelocation where a part of the further openings 8 is situated in thelacquer layer 6A and the photoresist layer 6B.

[0022] In a preferred embodiment of a device in accordance with theinvention, both the lacquer layer 6A and the photoresist layer 6B areaccordingly provided, at the location of the connection areas 4, 5 ofthe electronic component 2, 3, in this case the filters 2, 3, withfurther openings 8 wherein contact bumps 9 are situated on theconnection areas 4, 5. By virtue thereof, the device in accordance withthe invention can very suitably be used for so-called SMD (=SurfaceMounted Device) mounting. Preferably, the photoresist layer 6B comprisesa solder-repellent layer 6B. The same applies to the lacquer layer 6A.As a result, solder 9 can be readily used to form the contact bumps 9.

[0023] Preferably, the photoresist layer 6B comprises a solid foil layer6B. The same applies to the lacquer layer 6A. Such foils 6A, 6B can bereadily attached to the substrate 1 and to each other, and they have thedesired properties, i.e. a small degree of deflection, solder repellencyand photolithography processability. In this case, the invention isadvantageously applied to an acoustic wave filter 2, 3. As a result,this filter can be readily integrated with a semiconductor device 100,resulting in a device 1000 which can very suitably be used forapplications such as, for example, a mobile telephone. The device ofthis example is manufactured in the manner described hereinbelow using amethod in accordance with the invention.

[0024]FIGS. 3 through 7 are diagrammatic, perspective views of thedevice shown in FIG. 1 in successive stages of the manufacturing processusing a method in accordance with the invention. There is started from(see FIG. 3) a substrate 1 on which at least one electronic component 2,3, in this case two SAW filters 2, 3, is formed which is provided withone or more connection areas 4, 5. The filters 2, 3 are sealed off fromthe environment by means of a cover 6 on the component 2, 3, which coveris provided on the substrate 1 so as to form a cavity 7 above thecomponent 2, 3. This takes place (see FIG. 4) by providing a lacquerlayer 6A which, in this case, comprises a solid foil-comprisingphotoresist 6A which extends over the substrate 1 provided with thecomponent 2, 3. The lacquer layer 6A is subsequently (see FIG. 5)provided, using photolithography, with openings 7′ and further openings8 at the location of, respectively, the component 2, 3 and theconnection areas 4, 5 thereof. Subsequently, (see FIG. 6) a photoresistlayer 6B comprising a solid foil 6B is provided over the lacquer layer6A, said photoresist layer 6B sealing off the openings 7′, and thethickness of the cavities 7 formed being above zero.

[0025] Next, (see FIG. 7) further openings 8 corresponding to thefurther openings 8 in the lacquer layer 6A are formed in the photoresistlayer 6B at the location of the connection areas 4, 5, 11. Finally, (seeFIG. 1) contact bumps 9, in this case in the form of solder balls 9, areprovided in the further openings 8, on the connection areas 4, 5, 11.The device in accordance with the invention can now be subjected tofinal assembly; for example, as diagrammatically shown in FIG. 2, it canbe integrated with a semiconductor device 100 to form an electronicdevice 1000 which can suitably be used for mobile telephony. It will beclear that an important advantage of the invention resides in that itenables a large number of devices, only one of which is shown in theFigures, can be manufactured simultaneously.

[0026] The invention is not limited to the example describedhereinabove, and within the scope of the invention many modificationsand variations are possible to those skilled in the art. For example,components other than SAW filters can be used, for example MEMs (=MicroElectroMechanical Systems) such as a miniature electric motor or a Reedcontact. Consequently, it will be obvious that, in this application, anelectronic component is to be taken to include also an electric,electromechanical, optoelectronic or semiconductor component.

[0027] It is further to be noted that the further openings in thelacquer layer and the further openings in the photoresist layer can alsobe formed simultaneously, or the further openings in the lacquer layercan also be formed after the further openings in the photoresist layerhave been formed. In an important modification, a metal layer, such as athin aluminum foil, is situated on or below the photoresist layer. As aresult, a more sturdy cover and a better sealing of the component isobtained. Preferably, this metal layer is provided between the lacquerlayer and the photoresist layer. This metal layer can then be used as amask when openings are formed in the metal layer at the location of thefurther openings in the photoresist layer.

1. An electronic device comprising a body (10) including a substrate (1)on which at least one electronic component (2, 3) is situated, whichelectronic component is connected to one or more connection areas (4, 5)and is sealed off from the environment by means of a cover (6) on thecomponent (2, 3), which cover is provided on the substrate (1) and formsa cavity (7) above said component (2, 3), said cover (6) comprising afirst body (6A) which is situated on the substrate (1) and which isprovided, at the location of the component (2, 3), with an opening (7′),and said cover comprising a second body (6B) which is situated on thefirst body (6A) and closes the opening (7′), characterized in that thefirst body comprises a lacquer layer (6A), and the second body comprisesa photoresist layer (6B), and the lateral dimensions of the opening (7′)as well as the thickness and the material of the photoresist layer (6B)are chosen to be such that the thickness of the cavity (7) is above zerothroughout the surface of the component (2, 3).
 2. A device as claimedin claim 1, characterized in that the lacquer layer (6A) also comprisesa photoresist (6A), and further openings (8) are situated in the lacquerlayer (6A) and in the photoresist layer (6B) at the location of theconnection areas (4, 5) of the electronic component (2, 3), in whichopenings contact bumps (9) are situated on the connection areas (4, 5).3. A device as claimed in claim 1 or 2, characterized in that thephotoresist layer (6B) and, preferably, also the lacquer layer (6A)comprise a solder-repellent layer (6A, 6B).
 4. A device as claimed inclaim 1, 2 or 3, characterized in that the lacquer layer (6A) and thephotoresist layer (6B) comprise a solid foil (6A, 6B).
 5. A device asclaimed in any one of the preceding claims, characterized in that theelectronic component (2, 3) comprises a surface acoustic wave filter (2,3).
 6. A semiconductor device comprising a semiconductor body (100) witha substrate, and provided with one or more semiconductor elements,characterized in that the semiconductor device is provided with anelectronic device as claimed in any one of the preceding claims.
 7. Amethod of manufacturing an electronic device comprising a body (10)including a substrate (1) on which at least one electronic component (2,3) is formed, which electronic component is provided with one or moreconnection areas (4, 5) and is sealed off from the environment byproviding the component (2, 3) with a cover (6) on the substrate (1), acavity (7) being formed above the component (2, 3), said cover (6) beingformed by providing a first body (6A) on the substrate (1) and providingsaid body with an opening (7′) at the location of the component (2, 3),and by providing a second body (6B) on the first body (6A) in such a waythat the opening (7′) is closed, characterized in that the first body(6A) is formed by applying a lacquer layer (6A), and the second body(6B) is formed by applying a photoresist layer (6B) on top thereof, andthe lateral dimensions of the opening (7′) and the material used for thephotoresist layer (6B) are chosen to be such that the thickness of thecavity (7) is above zero throughout the surface area of the component(2, 3).
 8. A method as claimed in claim 7, characterized in that alsofor the lacquer layer (6A) use is made of a photoresist layer (6A), andfurther openings (8) are formed in the lacquer layer (6A) and in thephotoresist layer (6B) at the location of the connection areas (4, 5) ofthe electronic component (2, 3), in which openings contact bumps (9)containing a solder are formed on the connection areas (4, 5).
 9. Amethod as claimed in claim 7 or 8, characterized in that a solid foilcomprising solder-repellent layers is used for the lacquer layer (6A)and the photoresist layer (6B).
 10. A method as claimed in claim 7, 8 or9, characterized in that a surface acoustic wave filter (2, 3) is usedas the electronic component (2, 3).